The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
An opposed-piston engine includes an engine block defining one or more cylinders, a pair of pistons disposed within each cylinder, a crankshaft connected to each of the pistons, and one or more fuel injectors that inject fuel into each cylinder. Combustion of an air/fuel mixture within the cylinder causes the pistons to translate toward one another and away from one another, which drives rotation of the crankshaft. The engine block also defines an intake port that allows intake air to enter the cylinder, and an exhaust port that allow exhaust gas to be expelled from the cylinder.
In an opposed-piston two-stroke (OP2S) engine, the intake and exhaust ports typically extend through the sidewall of each cylinder and are disposed near opposite ends of the cylinder. When the pistons pass the intake and exhaust ports as the pistons are moving away from each other during a combustion or power stroke, intake air is drawn through the intake port while exhaust gas is expelled through the exhaust port. When the pistons pass the intake and exhaust ports as the pistons are moving toward each other during a compression stroke, the pistons prevent flow through the intake and exhaust ports. Since movement of the pistons controls flow through the intake and exhaust ports, there is no need for intake or exhaust valves.
Some opposed-piston four-stroke (OP4S) engines also control flow through the intake and exhaust ports using piston movement rather than intake and exhaust valves. In such an OP4S engine, intake air is drawn into the cylinder and exhaust gas is expelled from the cylinder at different times. Intake air is drawn into the cylinder when the pistons pass the intake and exhaust ports as the pistons move away from each other during an intake stroke. Fuel is injected into the cylinder, and the air/fuel mixture is compressed as the pistons move toward each other during a compression stroke. This compression causes the air/fuel mixture to ignite, and the combustion pressure urges the pistons to move away from each other during a combustion or power stroke. The pistons once again pass the intake and exhaust ports, and exhaust gas is expelled from the cylinder as the pistons move toward each other during an exhaust stroke.
Controlling flow through the intake and exhaust ports using piston movement limits the ability to adjust the timing and amount of flow through the intake and exhaust ports relative to controlling flow through the intake and exhaust ports using intake and exhaust valves. While attempts have been made to design an OP4S engine that controls flow through the intake and exhaust ports using intake and exhaust valves, the attempts have resulted in cost, manufacturing, assembly, and serviceability issues.